How do I find all UniversalTypes below another?

Use the field "children".

Using the field "children" you request UniversalTypes that are located deeper in the hierarchy. Use the field multiple times to dig deeper into the hierarchy.

UniversalTypes have for levels.

query utsBelowOther {
  utsearch(code: "UT05") {
    content {
      children {
        content {
        code
          children {
            content {
              code
            }
          }
        }
      }
    }
  }
}